Method for manufacturing energy storage device and energy storage device

A method for manufacturing an energy storage device according to one aspect of the present invention includes inserting an electrode assembly into a case while causing an insulating member having a sheet-like shape to follow a surface of the electrode assembly in which electrodes are layered. The insulating member includes a first portion corresponding to a first surface of the electrode assembly in a first direction which is a direction of a short side surface of the case and a thickness direction of the electrode assembly, a second portion corresponding to a first end surface which is an end surface of the electrode assembly in a second direction orthogonal to the first direction, a third portion corresponding to a second surface of the electrode assembly in the first direction, and a first extending portion extending from the first portion.